An actuator unit is used in a railway vehicle, for example, by being interposed between a vehicle body and a truck in order to suppress left-right direction vibration relative to an advancing direction of the vehicle body.
JP2010-65797A discloses an actuator unit including: a cylinder; a piston slidably inserted into the cylinder; a rod inserted into the cylinder and coupled to the piston; a rod side chamber and a piston side chamber defined within the cylinder by the piston; a tank; a first opening/closing valve provided on midway of a first passage that communicates the rod side chamber with the piston side chamber; a second opening/closing valve provided on midway of a second passage that communicates the piston side chamber with the tank; a pump that is configured to supply a working fluid to the rod side chamber; a motor that is configured to drive the pump; an exhaust passage that communicates the rod side chamber to the tank; and a variable relief valve provided on midway of the exhaust passage.
According to this actuator unit, a direction of thrust output thereby is determined by opening and closing the first opening/closing valve and the second opening/closing valve appropriately. By rotating the pump at a fixed speed using the motor, a constant flow is supplied into the cylinder, and meanwhile, by adjusting a relief pressure of the variable relief valve, a pressure in the cylinder is controlled. As a result, the actuator unit described above can output thrust of a desired magnitude in a desired direction.